Need construction tips on stairs and drainage

[Lilienberg]

Hello!

I have a newly built entrance staircase under which there is a basement room. The stairs will be clad in granite, but first a waterproof membrane needs to be applied in the form of a welded sheet. The sides of the staircase consist of plastered foam.

See image:


Next week, the roofer who is installing the waterproofing layer is coming, and he's wondering how it should be finished on the sides/ends of the stairs.

I'm not quite sure how to do it but have come up with the following options:

Option 1: Fold the sheet over the edge down onto the plaster. Advantage: tight and effective. The water that runs off doesn't crawl back under the sheet. Disadvantage: It's quite unsightly with a 10cm fold down on the sides as he suggests... can it be covered somehow?

Option 2: Install a base flashing/drip edge before the waterproofing is applied. Advantage: Water will drip down outside the plaster wall. Disadvantage: Quite unsightly... and how do you handle the vertical parts of the stairs (risers)?

Option 3: Let the sheet protrude 5cm from the staircase and then let the granite protrude just as much. Underneath, perhaps a small trim or silicone bead can be installed so that water running underneath drips down. Advantage: Probably looks quite nice. Disadvantage: Water might run back under the sheet and along the plaster.

Does anyone have tips or opinions on how to achieve this attractively?

I would like the appearance below... but in that case, no waterproofing has been used and the overhang on the stones is very small.